Weird shit happens in microwaves, and the list of shit you shouldn’t stick in a microwave is equally weird.  A little bit of internet research has let me to believe you should never stick any of the following in a microwave: a grape, an apple, a cell phone, a peep/marshmallow, jello, a smaller microwave, a pen, or a gremlin.  If you’re feeling adventurous, this guy offers some [likely unsafe and unwise/ do not try this at home-esque] microwave “fun-time” advice.